2019-05-09_REVISION - M1977300

• Permit No: M1977300
• IBM Index Class Name: REVISION
• Doc Date: 5/9/2019
• Doc Name: Request for Technical Revision
• From: Colorado Legacy Land
• To: DRMS
• Type & Sequence: TR28
• Email Name: MAC
• Media Type: D
• Archive: No

. COLORADO LEGACY LAND
4601 DTC Boulevard, Suite 120, Denver, CO 80237
T. [phone]
May8,2019
Mr.Michael Cunningham and Ms.Amy Eschberger
Division of Reclamation,Mining,and Safety
Department of Natural Resources
1313 Sherman Street,Room 215
Denver,CO 80203
Subject: Technical Revision#28: Revised North Waste Rock Pile Drainage Design,Construction,and
Schedule for Implementation
Mine Land Reclamation Permit M-1977-300,Schwartzwalder Mine,Golden,Colorado
Dear Mr.Cunningham:
Colorado Legacy Land, LLC (CLL) would like to revise Mine Land Reclamation Permit M-1977-300 for the
Schwartzwalder Mine,to include the following design,construction,and project schedule for a diversion pipeline
on the North Waste Rock Pile (NWRP). The primary goal of this project is to intercept and divert stormwater
from the ephemeral drainage above the NWRP,around the waste rock,and into Ralston Creek.
The previous site owner,Cotter Corporation N.S.L. (Cotter) submitted a design in Technical Revision #23 for a
diversion ditch. CLL is submitting Technical Revision #28, to revise this design and provide a schedule for
construction.
Drainage Design:
Table 1 summarizes the key differences between the previous design approved in Technical Revision #23 and
the current proposed design:
Table 1. ©esi Sum air and C >isals
crkvria Technical Revision#23 Teckdcal Revision#20
Design Flow 100- ear 67.7 cubic feet per second cfs 67.7 cfs
Area of Watershed 0.059 square miles 0.059 square miles
Aesthetics Above ground Below ground
Intake Concrete ditch Concrete headwall
Diversion Concrete and rip rap lined ditch Buried pipeline
The hydrology used for the design is the same hydrology used for Technical Revision #23,which used the SCS
Runoff Curve Number procedure. The SCS method predicts a 100-year runoff event will have a peak flow of 67.7
cubic feet per second(cfs). The primary difference between Technical Revision#23 and Technical Revision#28
are the aesthetics.
Drainage Construction:
The NWRP diversion pipeline consist of four primary components. Water from the ephemeral draining above
the NWRP is intercepted prior to running onto the NWRP at a headwall. From the concrete headwall water enters
a 30-inch pipe which runs adjacent to the NWRP access road. At the base of the NWRP, the water enters a
manhole and flows into a 42-inch pipe before discharging into Ralston Creek.